Types of Australian Opal — Black, Crystal, Boulder & More

Black opal

Black opal is the most valuable variety of precious opal. The term refers not to a black colour, but to a dark body tone — the underlying base on which the spectral fire plays. On the body-tone scale (see our body tone guide), black opal sits at N1 to N4: anything from nearly opaque black through to a dark grey base.

The dark base is what makes black opal so prized. Bright spectral colours — reds, greens, blues, the full play-of-colour — appear far more vivid against a dark background than they do against a light one. The same fire on a light base would still be beautiful, but it would not have the same depth or contrast.

Black opal is mined almost exclusively at Lightning Ridge in north-western New South Wales. A handful of other fields have produced isolated stones with dark body tones, but Lightning Ridge has supplied the bulk of the world's black opal for more than a century. Within Lightning Ridge there are sub-fields — the town itself, Coocoran, Carters Rush, Mulga Rush, Grawin, Wyoming, Jagg Hill and others — each with characteristic colour, brightness and structure.

Crystal opal

Crystal opal is precious opal that is transparent or semi-transparent — you can see through the body of the stone, with the play-of-colour appearing throughout its depth rather than only on the surface. The body tone can be anywhere from light to dark.

The defining property is clarity. A high-clarity crystal opal with vivid fire viewed from any angle is one of the most three-dimensional gems in the precious-stone world; the colour appears to float within the body of the stone. Crystal opal is mined at Coober Pedy, Mintabie and Lightning Ridge, with the Coober Pedy region historically producing the largest volume.

A black crystal is a crystal opal that also has a dark body tone (N1–N4). These are the rarest precious opals on earth and command the highest per-carat prices.

Boulder opal

Boulder opal is precious opal that forms in thin veins or pockets within ironstone — a hard, dark brown sedimentary rock. When the stone is cut, the natural ironstone is left as the backing, so the finished gem is part opal, part dark host rock. The ironstone backing provides a natural dark background that intensifies the opal's play-of-colour, with the visual effect comparable to a dark-bodied opal.

Boulder opal is mined exclusively in central-western Queensland — principally around Quilpie, Yowah, Winton and Koroit. Each field has a distinctive character: Yowah is famous for its “nut”-style opal-filled nodules, Koroit for its swirling matrix patterns, Quilpie for clean colour bars.

Because the opal layer is integral to the host rock, boulder opal is typically not graded on the same body-tone scale as solid opal. It is graded on the brightness and pattern of the opal face, the proportion of ironstone backing, and the consistency of colour.

Light opal

Light opal — sometimes called “white opal” or “milky opal” — is precious opal with a light-coloured body tone (N7–N9 on the standard scale). It is the most abundant variety of Australian precious opal.

The colour-play in light opal is set against a pale or milky background, giving a softer, more pastel appearance than black opal. Quality light opal still commands strong prices, particularly when the fire is bright, the pattern is large, and the body is clean. Most light opal comes from Coober Pedy, Mintabie and Andamooka in South Australia.

Matrix opal

Matrix opal refers to opal that is dispersed through the host rock in tiny seams, rather than forming a clean layer. The finished stone shows the opal's colour-play across a mottled rock face. Andamooka in South Australia is the best-known source of true matrix opal.

Most natural matrix opal is paler than the host rock alone would suggest. A traditional treatment known as “Andamooka treatment” uses a sugar and acid process to darken the host stone, intensifying the apparent contrast. Treated matrix should always be disclosed at sale; we do not stock undisclosed treated stones.

Other types and terminology

• Dark opal — opal with body tone in the N5–N6 range; darker than light opal but not dark enough to be called black. Sometimes marketed as “semi-black”.
• Doublet — a thin slice of natural opal bonded to a dark backing (commonly ironstone or potch) to imitate the appearance of a solid black opal. Doublets and triplets are legitimate products but must be disclosed.
• Triplet — a doublet with an additional clear cap (usually quartz) on top, for durability.
• Potch — non-precious opal: opal without colour-play. Often present alongside precious opal in the same seam.
• Synthetic / lab-grown opal — chemically the same as natural opal but produced in a laboratory. Always disclosed in reputable trade.

How value is determined

Across all types, the value of a precious opal is determined by a small number of factors:

1. Body tone — darker bases (toward N1) carry a premium for solid opal.
2. Brightness of the play-of-colour. Brightness is the single most important factor across all opal categories; a bright N7 light opal will often outperform a dull N3 black opal.
3. Colour balance — opals with a full spectrum (especially containing red) are more valuable than those limited to greens and blues.
4. Pattern — named patterns such as harlequin, flagstone, ribbon and broad-flash are rarer and more valuable than pinfire.
5. Carat weight and shape — larger, well-cut stones with traditional shapes (oval, drop) are more readily set into jewellery and command stronger prices.
6. Provenance and certification — first-hand sourcing and reliable certification add real value, especially at wholesale.

For the technical scales we use across our inventory — body tone, dome profile, brightness, shape and origin — see our classification tables. To browse current available stock by category, use Quick Search.